Roc Nation Sports -- Rejected By Three More Boxing Champs

Jay Z's Roc Nation Sports is trying to change the game of professional boxing ... courting three of the biggest stars in the sweet science to join RNS' exploding roster, TMZ Sports has learned.

Of course, Jay recently inked boxing superstar Andre Ward and made a serious push to sign former world champ Adrien Broner ... but AB rejected the 5-year $40 million offer.

Now, we've spoken with three other major fighters who have also been contacted by Roc Nation ... more evidence that Jay is dead serious about making a splash in the boxing world.

The fighters -- who wished not to be named -- tell us that just like Broner's courting, Jay Z never personally reached out ... sending his people to make contact instead and we're told it rubbed the fighters the wrong way.

All three fighters we spoke with tell us they ultimately turned down the Roc Nation offers ... but aren't closing the door on a possible relationship with RNS in the future.

Meantime, Roc Nation Sports is still growing like crazy ... and recently signed Georgia running back Todd Gurley who's expected to be one of the first running backs selected in the NFL Draft.